Java 扫描仪工作不正常
各位程序员好。我还有一个困扰我的问题。我试图从用户处接收输入，但总是收到“java.util.NoSuchElementException:找不到行”。我尝试了我所寻找的所有方法，但没有成功。这是我的密码：Java 扫描仪工作不正常,java,exception,java.util.scanner,Java,Exception,Java.util.scanner,各位程序员好。我还有一个困扰我的问题。我试图从用户处接收输入，但总是收到“java.util.NoSuchElementException:找不到行”。我尝试了我所寻找的所有方法，但没有成功。这是我的密码： import java.util.Scanner; import java.io.*; public class UserLog { static String username; static String password; static String pass
import java.util.Scanner;
import java.io.*;
public class UserLog {
static String username;
static String password;
static String passcompare;
static File name;
static String Userfile = "username-";
static String Passfile = "password-";
public static void main(String[] args) {
menu();
}
public static void menu(){
boolean call = false;
try (Scanner in = new Scanner(System.in)) {
do {
System.out.println("Select an option: ");
System.out.println("1: New account \n"
+ "2: Existing account");
System.out.print("-");
int choice = in.nextInt();
in.nextLine();
switch(choice) {
case 1:
call = true;
System.out.println("\nNew account called\n");
userCreate();
break;
case 2:
call = true;
System.out.println("\nExisting account called\n");
login();
break;
default:
System.out.println("\nNot a valid option\n");
}
} while(!call);
in.close();
}
catch(Exception ex) {
System.out.println("Exception Text: " + ex);
}
}
static void login(){
try (Scanner in = new Scanner(System.in)) {
System.out.println("LOGIN SCREEN\n");
System.out.print("Username: ");
username = in.nextLine();
name = new File("user-" + username + ".txt");
if(name.exists()) {
System.out.println("Username exists");
System.out.print("Password: ");
password = in.nextLine();
//scans userfile for password
if(password.length() != 0 && password.length() >= 8 /* and password-username match */) {
System.out.println("Login successful");
in.close();
}
}
else {
System.out.println("Username doesn't exist in system");
System.out.println("Would you like to create this user? (y/n)");
System.out.print("-");
char choice = (char)System.in.read();
switch(choice) {
case 'Y':
case 'y':
System.out.println("Creating user " + username);
name = new File("user-" + username + ".txt");
name.createNewFile();
System.out.println("User created");
passCreate(name);
in.close();
break;
case 'N':
case 'n':
System.out.println("Denied creation of user");
in.close();
break;
default:
System.out.println();
}
}
in.close();
} catch (IOException ex) {
System.out.println("Exception Text: " + ex);
}
}
private static File nameCreate() {
try (Scanner user = new Scanner(System.in)) {
System.out.print("Enter Username: ");
username = user.nextLine();
name = new File("user-" + username + ".txt");
if(!name.exists()) {
name.createNewFile();
try (FileWriter fw = new FileWriter(name)) {
fw.write(Userfile + username + "\n");
fw.write(Passfile);
fw.flush();
fw.close();
}
catch(Exception ex) {
System.out.println("Exception Text: " + ex);
}
//puts lines of text in the file-
//username-"username"
//password-
//
System.out.println("User Created\n");
}
else if(name.exists()) {
System.out.println("User already exists\n");
nameCreate();
}
user.close();
}
catch(Exception ex) {
System.out.println("Exception Text: " + ex);
}
return name;
}
private static void passCreate(File user) {
username = user.toString();
System.out.println(username + "\n");
boolean code = false;
try (Scanner pass = new Scanner(System.in)) {
do{
//opens file and reads until line "password-" and appends it with created password once confirmed
System.out.println("Create a password");
System.out.print("Password: ");
password = pass.nextLine();
if(password.length() >= 8) {
System.out.print("Confirm Password: ");
passcompare = pass.nextLine();
if(password.equals(passcompare)) {
code = true;
System.out.println("Passwords match\n");
//stores password
}
else {
System.out.println("Passwords don't match\n");
}
}
else {
System.out.println("Password needs to be longer than 8 characters\n");
}
}while(!code);
pass.close();
}
catch(Exception ex) {
System.out.println("Exception Text: " + ex);
}
}
private static void userCreate() {
nameCreate();
passCreate(name);
}
}
我知道这是丑陋和不完整的，但这个问题使我无法继续前进。如果通过“现有用户”选项并以这种方式创建用户，则可以创建密码，但如果尝试通过“创建新用户”，则会出现无行异常。我的问题是：如何为扫描仪创建更多的行以创建密码，或者我还有什么其他选项来完成此任务。我试过hasNextLine（），这让我意识到没有更多的行了。谢谢关闭
扫描器输入流NoTouchElementException扫描仪- 创建一个用于所有方法的
扫描仪实例 - 不要关闭
扫描仪 - Java是一种
语言。使用非静态方法OO
public class UserLog {
private String username;
// more variables...
private final Scanner in;
public UserLog() {
in = new Scanner(System.in);
}
public static void main(String[] args) {
UserLog userLog = new UserLog();
userLog.showMenu();
}
public void menu() {
boolean call = false;
do {
try {
System.out.println("Select an option: ");
System.out.println("1: New account \n" + "2: Existing account");
System.out.print("-");
int choice = in.nextInt();
in.nextLine();
switch (choice) {
case 1:
call = true;
System.out.println("\nNew account called\n");
userCreate();
break;
case 2:
call = true;
System.out.println("\nExisting account called\n");
login();
break;
default:
System.out.println("\nNot a valid option\n");
}
} catch (InputMismatchException e) {
System.out.println("Invalid option " + in.nextLine());
}
} while (!call);
}
...
}
是否可以只向我们显示与
NoTouchElementException扫描仪。但在选项1中，您获得用户名，关闭扫描仪
，然后尝试使用系统制作另一个扫描仪
。在
中输入密码。我明白了。谢谢你的链接。它澄清了这一点，从来没有想到这一点。因此，如果我们使用扫描仪从System.in读取，我们不应该关闭扫描仪，因为底层流也会被关闭？在这种情况下，一个愚蠢的后续问题是：有没有办法重新初始化（重新打开）系统。在
中使用标准输入流？不，只是不要关闭扫描仪
，所以我基本上删除了所有的.close（）这是一个很好的例子。但是需要抛出的异常太多了。这是由于静态方法造成的，还是仅仅因为它是如何产生的？对不起，现在很晚了，你怎么才能让这一切都变成非静态的呢？